In filter apparatus of the type disclosed in U.S. Pat. Nos. 4,090,965 and 4,639,315 web filter material is mounted on a rotatable filter frame to form one or more enclosed filter effluent compartments on the rotatable frame. During filtering, liquid influent containing suspended solids is passed into an influent tank and flows in a filter direction through the filter material into a filter effluent compartment for discharge to an outlet. The filter material on the filter frame is intermittently backwashed by rotating the filter frame past a suction head which is positioned to engage the outer side of the filter material and which is operative to draw filtered liquid from inside the filter effluent compartment through the filter material in a direction opposite the filter direction, to remove and discharge entrapped solids in the backwash water. The above patents also disclose a high pressure spray wash for washing the filter material after a number of backwash operations. The high pressure spray wash includes spray nozzles disposed either inside or outside the filter effluent compartment and arranged to direct high pressure liquid spray at one side of the filter material. However, the high pressure spray wash cannot be effected while the filter material being washed is submerged in liquid and, in the prior filter apparatus of this type, it was necessary to drain down the liquid in the tank to a level sufficient to enable spray washing. This substantially increased the overall time required for a high pressure spray washing of the drum and correspondingly increased the amount of time that the filter apparatus was out of its filtering mode.